1. Field of the Invention
This invention generally relates to multi-node communication or computer networks, and more specifically, the invention relates to establishing connections or links between nodes of such networks.
2. Background Art
In many multi-node communication systems, such as computer systems having a Systems Network Architecture (SNA), links must be established between two nodes of the system before these nodes can fully communicate with each other. Various standard procedures are known for establishing these links. These known procedures include EEDLC (Enterprise Extender Data Link Control) and LLC2 (Logical Link control type 2).
In these procedures, a first, or primary, node, trying to connect with a second, or secondary, node, will attempt to determine the availability of that secondary node. Each of these nodes may also attempt to determine various parameters of the other node such as node type, Node ID, Link Station role etc. Still other parameters, maximum I-field length that sender can receive, may be negotiated during the connection attempt. If the second node is ready, willing and able to work with the first node, a successful connection between the nodes may be established. However, if the two nodes are not able to communicate together, the second node may send to the first node a message indicating a failed connection attempt.
In these connection efforts, numerous messages may be exchanged between the nodes during the connection effort. In the existing scenario, both the primary (mainframe side) node and secondary (SNA node) node starts with a TEST command (followed by a NULL XID in case of LLC2) or a NULL XID (in case of EEDLC). Then both the partners send XID's back and forth before establishing the link. The reason for sending multiple XID's is that, the XID state is progressively moved from one state to the next after receiving a positive response from the partner.
FIG. 1 shows, as an example, the requests, responses and negotiations that may be exchanged between two nodes as they attempt to establish a connection. As can be seen, a multitude of messages are needed. These messages may consume considerable bandwidth. In addition, a significant amount of time may be needed before all the messages and negotiations are completed. There is no known solution to reduce these XID flows.